29. With a doubling of atmospheric CO2, it is likely that there will be increases in the thickness of the active layer permafrost and the disappearance of most of the ice-rich discontinous permafrost over a century-long time span. This figure provides a good example of changes already observed in Alaska. Widespread loss of discontinous permafrost will trigger erosion or subsidence of ice-rich landscapes, change hydrologic processes, and release CO2 and methane to the atmosphere. Changes in the cryosphere will reduce slope stability and increase incidence of natural hazards for people, structures and communication links. Buildings, roads, pipelines and communication links will be threatened.